Fundamentals　of　current　conduction　of　the　AlGaN/GaN　HEMTs　have　been　studied　under　the　temperature　ranging　from　26C　to　250C.　It＇s　found　that　the　maximum　drain-source　current　(IDS)　decreases　with　rising　temperature,　and　the　temperature　dependent　of　IDS　has　a　negative　coefficient　of　0.31　mA/mm　C.　This　deterioration　mainly　cause　by　decreasing　in　mobility.　And　a　rise　in　temperature　is　accompanied　with　an　increase　in　barrier　height　and　a　reduction　in　ideality　factor.　Mechanisms　are　suggested,　including　thermionic　emission,　field　emission,　trap-assisted　tunneling　and　so　on.　It＇s　also　found　that　reverse　leakage　current　increases　first　and　then　decreases　with　rising　temperature,　and　the　dominant　mechanisms　are　the　effects　of　piezoelectric　polarization　field　and　variation　of　two-dimensional　electron　gas　charge　density.　The　remarkable　finding　is　that　breakdown　voltage　has　a　trend　opposite　to　that　of　the　reverse　leakage　current,　and　the　minimum　occurred　at　around　175C.　©　2011　IEEE.